This is like three years late I know but the version of Howard the Duck that you see here is from the main Marvel continuity whereas the zombie Howard that was killed in "Marvel Zombies vs Army of Darkness" was different from the main Howard because if you don't know, Marvel, like most comic companies, has multiverse and with this multiverse, they're able to explore ideas that would be considered stupid, ridiculous or canon-breaking which includes Marvel Zombies with its official universe designation being "Earth-2149" while the main universe's designation is "Earth-616".